Design of nondispersion optical feedback system using diffraction grating for semiconductor laser multiple longitudinal modes control

The external optical feedback system with a diffraction grating and mirrors is designed as a light source system in wavelength division multiplexing transmission. This system can select not only oscillation center wavelength but also spectral range in semiconductor lasers by using an identical grating twice. Experimental results demonstrate selected oscillations of single and double longitudinal modes in a multimode semiconductor laser.     

Scanning the laser gain spectrum using distributed feedback and hydrostatic pressure

High-pressure measurements on distributed-feedback GaxIn1-xASyP1-y lasers allow the gain spectrum to be scanned, providing a powerful tool for the study of the intrinsic properties of the laser, including the mechanisms responsible for the high-temperature sensitivity.     

Single-mode operation characteristics of a self-injection seededFabry-Perot laser diode with distributed feedback from a fiber grating

We study the operational characteristics of a self-injection seeded laser diode in an external cavity consisting of a fiber Bragg grating. The distributed feedback (DFB) of light in the grating provides an additional tolerance of frequency detuning in mode selection. The spectral characteristics at different operating frequencies and feedback rates have been investigated. Wavelength tuning has also been realized by applying compressive and tensile strain to the grating and a tuning range of 11.6 nm has been obtained     

Broad-stripe near-diffraction-limited mid-infrared laser with a second-order photonic-crystal distributed feedback grating

Electron-beam lithography was used to pattern a second-order photonic-crystal distributed feedback grating onto an antimonide type-II "W" laser emitting at /spl lambda//spl ap/3.7 /spl mu/m. For pulsed optical pumping, the output beam was essentially diffraction-limited up to a stripe width of 150 /spl mu/m, and remained no worse than eight times the diffraction limit for stripes as wide as 600 /spl mu/m. This represents a considerable improvement over all previous mid-infrared semiconductor lasers with such broad stripes.     

紧凑型光栅外腔可调谐半导体激光器

研制了一台结构紧凑的窄线宽、可调谐半导体激光器.采用光栅外腔Littrow结构,将光栅和平面反射镜置于同一个旋转平台上,并使光栅衍射平面和平面镜反射平面的交线与平台旋转轴重合,通过旋转平台实现光栅外腔选取单纵模、压窄线宽和波长调谐,并保证输出光的方位不发生改变,同时用棱镜将输出光斑压缩成为类方形.该激光器的尺寸为110 mm×80 mm×35 mm,中心输出波长为653 nm,谱宽0.07 nm,调谐范围4.6 nm,可连续稳定运转4小时以上.     

Zero-power gain measurements in a CW HF laser using a pulsed-probe laser

Zero-power gain measurements in a supersonic diffusion-type CW HF laser have been made using a pulsed HF probe laser. A peak zero-power gain of 10 percent/cm was measured on aP_{2}(3)vibrational-rotational transition and 7 percent/cm on aP_{1}(6)transition for flow rates corresponding to 1.8 kW of closed-cavity power. The variation of zero-power gain with rotational quantum numberJfits a simple rotational equilibrium model indicating increasing rotational temperatures with increasing distancexfrom the nozzle exit plane. The model also indicates a total inversion forx leq 0.2in for theP_{2}(J)transitions and a partial inversion further downstream.     

Degradation analysis in asymmetric sampled grating distributed feedback laser diodes

This paper presents the experimental observation of the degradation in asymmetric sampled grating DFB lasers by the accelerated life tests. Two degradation phenomena related to the electrical characteristics of LDs are observed during the tests. The first degradation phenomenon by increasing the reverse current is considered as a formation of leakage current path enough to prevent lasing operation in lateral blocking layer near active region of lasers. The second degradation phenomenon by decreasing the forward current is considered as activation of non-radiative Auger recombination process by thermal energy. It is also experimentally observed that the second degradation phenomenon is recovered after remained in room temperature with no electrical stress. Therefore, the criteria for LD reliability can be determined by observing the degradation of the reverse current–voltage characteristics.     

Wideband gain flattened erbium fibre amplifier using a photosensitive fibre blazed grating

An erbium fibre amplifier with a highly flattened gain spectrum is demonstrated for the first time using an all fibre photosensitive Bragg grating. An ASE spectrum flattened to within +or-0.5 dB over a bandwidth of 35 nm in the 1550 nm window is achieved with a 3 mm long radiation coupling Bragg fibre grating.<>     

Electrical control of the distributed feedback organic semiconductor laser based on holographic polymer dispersed liquid crystal grating

In this paper, we demonstrate the electrical control of the distributed feedback (DFB) organic semiconductor laser based on a holographic polymer dispersed liquid crystal (HPDLC) grating for the first time. The grating is fabricated on the top of the organic semiconductor film to act as an external feedback structure. Experimental results show that the lasing intensity can be decreased by increasing the external electric field, and the lasing wavelength exhibits a slight blue-shift of 1.4 nm during the modulation process, indicating a good stability. The modulated performances are attributed to the decreases in the refractive index modulation and average refractive index of the HPDLC grating respectively as a result of the field-induced liquid crystal reorientation. This study provides some new ideas for the improvement of DFB organic semiconductor laser to enable envisioned applications in laser displays and integrated photonic circuits.     

Approximate analysis of gain saturation of a distributed feedback laser with end reflectors

An approximate method for the analysis of distributed feedback lasers is presented. An expression for the small-signal gain coefficient αoNas a function of the output power PNoutnormalized to the saturation power Ps, coupling coefficientk, complex reflectivity of the end reflectorsR, and length of the laserLis obtained. The results are found to be in good agreement with published computer solutions.     

基于衍射光栅耦合输出的一级分布反馈太赫兹量子级联激光器

对比研究了两种不同结构太赫兹波段的双金属波导一级分布反馈量子级联激光器(THz-DFB-QCL).提出并实现基于衍射光栅耦合输出的THz-DFB-QCL中,太赫兹波通过衍射光栅而非解理腔面形成出射.计算表明,优化衍射光栅的结构可实现约70%的激光输出效率和小于1%的反射率,激光发散角约为10°×50°.极低的反射率可以有效抑制反射波对腔内谐振的干扰,是获得单模激射的关键.实验上,利用衍射光栅耦合输出的激光器实现了频率约2.58 THz的稳定单模激光,边模抑制比达23 dB,光束分布与理论计算相吻合.得益于较好的衍射效率和光束准直性,相比于常规的解理腔面边发射激光器,通过衍射光栅耦合输出显著提升了激光功率.     

Identification of linear time-invariant system using feedback gain

Feedback property and exponential curve fitting are used to identify the parameters of transfer function. It is assumed that all state variables are inaccessible for measurement.     

Transverse mode control in a distributed feedback semiconductor laser

Transverse modes in a distributed feedback semiconductor laser are discussed. A scheme for discriminating these modes is suggested.     

Fiber laser polarization tuning using a Bragg grating in a Hi-Bifiber

Single- and dual-wavelength tunable lasing (around 1552 nm) has been obtained in an Er-doped low-Bi fiber laser with a Bragg grating mirror in a Hi-Bi fiber. Equal output powers for both laser lines and spectral spacing of up to 0.26 mm, larger than the original spacing between the resonance peaks of the grating (0.2 nm), can be easily achieved by employing a polarization controller inside of the laser cavity     

808nm DFB半导体激光器的光栅制备

实验优化设计了808nm DFB半导体激光器的二级布拉格光栅结构,介绍了808 nm分布反馈（DFB）半导体激光器光栅制备的工艺过程。采用全息光刻方法和湿法腐蚀技术在GaAs衬底片上制备了周期为240nm的光栅图形,全息光刻系统采用条纹锁定技术降低条纹抖动和提高干涉稳定性,腐蚀液采用H3PO4 : H2O2 : H2O (1 : 1 : 10),腐蚀时间为30s。光学显微镜、扫描电子显微镜（SEM）和原子力显微镜（AFM）测试显示,光栅周期为240nm,占空比为0.25,深度为80nm,具有完美的表面形貌,及良好的连续性和均匀性。     

具有表面二阶金属光栅的927nm分布反馈半导体激光器的研制

采用全息光刻和湿法腐蚀光栅技术,成功制备了表面二阶金属光栅宽条型分布反馈（DFB）半导体激光器,无需二次外延生长过程,实现了宽接触室温直流下大范围稳定单纵模工作。腔面未镀膜器件,在脉冲工作条件下,注入电流为2．28A时,单面输出功率大于600mW,斜率效率达0．37mW／mA,功率效率大于11％。在连续电流注入下,当注...     

用前腔面“泄漏激光”作为监控信号的AlGaAs/GaAs光纤耦合激光器

本文报导用前腔面“泄漏激光”作为监控信号的新方法。这种分光方式没有插入损失,跟踪线性。初步结果表明,它能满足目前通信系统自动光功率控制的要求。     

Narrow line semiconductor laser using fibre grating

A narrow linewidth, low chirp, wavelength selectable, packaged alternative to current DFB structures has been developed which employs a fibre reflection grating incorporated in the fibre pigtail. The wavelength of the packaged device can be determined by the appropriate choice of fibre grating coupled to the antireflection coated facet of a 1.55 mu m BH laser. Linewidths of less than 50 kHz, sidemode suppression of more than 30 dB and chirp when modulated at 1.2 Gbit/s of <0.5 MHz have been demonstrated.<>     

Characteristics of a semiconductor laser coupled with a fiber Bragg grating with arbitrary amount of feedback

Stationary characteristics (such as laser frequency at threshold, light-intensity curve, etc.) and relative intensity noise of laser diodes coupled with an external Bragg reflector are studied for arbitrary amount of optical feedback. We put the stress on the interplay between external and internal cavities when the feedback strength is increased. For strong feedback, new stationary solutions that do not exist in the case of conventional feedback appear, while the ellipse, which usually contains the modes and so-called antimodes, collapse in the plane frequency-gain. Finally, analytical expressions are compared with numerical results obtained through a new approach that uses Green functions.     

Dynamic output feedback sliding-mode control using pole placement and linear functional observers

This paper presents a methodological approach to design dynamic output feedback sliding-mode control for a class of uncertain dynamical systems. The control action consists of the equivalent control and robust control components. The design of the equivalent control and the sliding function are based on the pole-placement technique. Linear functional observers are developed to implement the sliding function and the equivalent control. Stability of the resulting system under the proposed control scheme is guaranteed. A numerical example is given to demonstrate its efficacy.